1. Field
The embodiments discussed herein relate to a transfer device that transfers an image to printing media and an image forming apparatus having the same.
2. Description of the Related Art
An electrophotographic image forming apparatus, which is a kind of image forming apparatus, irradiates light onto photoconductors charged with a designated potential to form electrostatic latent images on the surfaces of the photoconductors, and supplies developers to the electrostatic latent images to form developer images. The developer images formed on the photoconductors may be transferred to a printing medium through a transfer unit, and the developer images transferred to the printing medium pass through a fixing process and discharged to the outside of the image forming apparatus.
In such an image forming apparatus, developing cartridges for corresponding developers for respective colors may be disposed in parallel, and developer images for respective colors overlap with each other by the photoconductors of the respective developing cartridges and respective transfer rollers corresponding thereto to form a color image. Further, in the image forming apparatus, the developing cartridge corresponding to black from among the developing cartridges is operated to form a monochrome image.
If the monochrome image is formed, the photoconductors of the developing cartridges corresponding to colors, except for black, do not need to be operated. Therefore, the photoconductors corresponding to colors, except for black, are not rotated, and the transfer rollers corresponding to these photoconductors are separated from the photoconductors, thereby extending a lifespan of the photoconductors.
Such an image forming apparatus may be changed between three modes, e.g., a ready mode in which a transfer nip between a transfer belt and the photoconductors is not formed, a mono mode in which only a transfer nip of a single color between the transfer belt and one photoconductor is formed through contact, and a color mode in which transfer nips of plural colors between the transfer belt and plural photoconductors are formed through contact. In order to change the image forming apparatus between the three modes, cams and sliders may be used as a mode conversion device for form/release the transfer nips.
In case of such a mode conversion device, two or more cam members may be provided on the same shaft, and as the cams are rotated, the sliders move by the cam members and links connected to the sliders move positions of the transfer rollers of the respective colors, thereby achieving mode conversion among these three modes.
When the cams are rotated, the different cam members having the same phase on the same shaft are simultaneously rotated and simultaneously cause friction with the different sliders, thereby increasing cam driving load.
That is, in order to form/release transfer nips between the photoconductors and the transfer belt, the different cam shapes having the same phase on the same shaft are simultaneously rotated, and thus a friction load between a mono cam shape and a mono slider and friction load between a color cam shape and a color slider may be simultaneously generated and are added to increase cam driving load. A reason for this is that when the color cam and the mono cam move the corresponding sliders, the phases, where the cam shapes reach the top dead centers, are the same.
That is, a time when the mono cam is rotated, contacts the mono slider and maximally pushes the mono slider, and a time when the color cam is rotated, contacts the color slider and maximally pushes the color slider are the same, and thus loads generated when the cams respectively push the corresponding sliders overlap with each other to increase cam driving load.
When the cam driving load is increased, the capacity of a motor driving the cams needs to be increased and the increase in the capacity of the motor raises costs and increases a set size. Further, when the cam driving load is increased, the lifespan of the mode conversion device to form/release transfer nips is lowered, reliability in joint and abrasion is lowered, and thus the lifespan of the transfer device is